Dispersion of metal nanoparticles, method for producing the same, and method for synthesizing metal nanoparticles

Abstract

The present invention aims to provide a method for producing a dispersion of metal nanoparticles which enables to control the shape and the particle diameter over a wide range, a dispersion of metal nanoparticles having superior dispersion stability, and a method for producing the same. In addition, the present invention further aims to provide a dispersion of metal nanoparticles which has a volume resistivity of 2×10 −6 to 6×10 −6 Ω·cm and is suitable for use as an electrically conductive material, and a method for producing the same. Moreover, the present invention further aims to provide a method for synthesizing metal nanoparticles which can produce metal nanoparticles suitable for use as electrically conductive materials by synthesizing the metal nanoparticles from a insoluble metal salt which is free of corrosive materials.

The invention claimed is: 
     
       1. A method for synthesizing metal nanoparticles, comprising the steps of:
 preparing an aqueous metal salt solution (A) by dissolving a metal salt, said aqueous metal salt solution (A) consisting essentially of the metal salt and a solvent; 
 preparing an aqueous carboxylic acid solution (B) by dissolving one type or two or more types of compounds selected from the group consisting of, citric acid, maleic acid, and salts thereof; 
 preparing an aqueous reducing agent solution (C) by dissolving one type or two or more types of compounds selected from the group consisting of formic acid and salts thereof; 
 mixing the aqueous carboxylic acid solution (B) with the aqueous metal salt solution (A) so as to obtain a suspension of a carboxylic acid salt in which poorly-soluble carboxylic acid salt precipitates; and 
 forming metal nanoparticles by adding and mixing the aqueous reducing agent solution (C) with the suspension of the carboxylic acid salt, 
 wherein the aqueous solutions (A), (B), and (C) are separately prepared, 
 metal elements contained in the metal salt comprise 75% by mass or more of silver, and 
 the mixing with the aqueous reducing agent solution is carried out by stirring at a temperature of 25 to 95° C. 
 
     
     
       2. The method for synthesizing metal nanoparticles according to  claim 1 , wherein one type or two or more types of metals selected from the group consisting of gold, platinum, palladium, and ruthenium are included as the remainder of the metal elements contained in the metal salt of the aqueous metal salt solution (A) other than silver. 
     
     
       3. The method for synthesizing metal nanoparticles according to  claim 1 ,
 wherein an amount of carboxylic acid, an amount of carboxylic acid salt, or a total amount of carboxylic acid and carboxylic acid salt contained in the aqueous carboxylic acid solution (B) is within a range from 0.3 to 3.0 mol relative to 1 mol of the metal element contained in the aqueous metal salt solution (A), and 
 an amount of reducing agent contained in the aqueous reducing agent solution (C) is within a range from 0.1 to 3.0 mol relative to 1 mol of the metal element. 
 
     
     
       4. A method for producing a metal film, comprising the steps of:
 obtaining a dispersion of metal nanoparticles by dispersing the metal nanoparticles which are obtained by the synthesis method according to  claim 1  in a dispersion medium; and 
 forming a metal film by coating the dispersion of metal nanoparticles as a composition for producing a metal film on a base material by a wet coating process.